Hydrothermal/Ionothermal Synthesis, Properties And Applications Of Hierarchical Alkaline-earth Metal Borates Architectures

Hierarchical three-dimensional(3D) structures with unique morphology and well-defined porous networks at multiple scales have been paid considerable attention in diverse fields owing to their unique size-/morphology-dependent physico-chemical properties. Although the boron and alkaline-earth metals resources are abundant, the exploitation and utilization of them were still at the primary stage, how to utilize them efficiently is an urgent issue to be solved. The nanostructured borates with unique morphology have drawn much research interests and substantial efforts for their versatile applications in various fields. Herein, hierarchical 3D alkaline-earth metal borate nanoarchitectures were synthesized by hydrothermal or ionothermal methods which followed by mild thermal conversion. The as-obtained 3D nanoarchitectures were employed in the treatment of simulated wastewater containing heavy metal ions and heterogeneous catalysis, this expanded the applications of metal borates and promoted the comprehensive utilization level of the boron and alkaline-earth metals.Hierarchical porous MgBO2(OH) superstructures, synthesized for the first time by an ionothermal route using ionic liquids as solvents, leading to the hierarchical porous Mg2B2O5 superstructures after thermal conversion. The formation of the porous MgBO2(OH) superstructures was attributed to the synergistic effect of the hydrophilic surfaces of the MgBO2(OH) and the ionothermally confined self-organization. The specific surface areas of the hierarchical porous MgBO2(OH) and Mg2B2O5 superstructures were 57.22 and 24.20 m2g-1, respectively, both of which exhibited good adsorption performance and excellent recyclability when used as adsorbents for the removal of CR from the simulated waste water. The adsorption of CR onto the MgBO2(OH) / Mg2B2O5 superstructures was fitted well with Langmuir isothermal model, giving rise to the maximum adsorption capacities(qm) for CR as 228.3 and139.3 mg g-1, respectively. In addition, the hierarchical porous Ca(BO2)2 microspheres were successfully obtained by the hydrothermal-thermal conversion method. When employed as the adsorbents for the removal of the heavy metal ions such as Pb2+ and Cd2+, the qm were confirmed by using the Langmuir isothermal model as 114.2 and110.6 mg g-1, respectively. Moreover, when Pd nanoparticles were loaded onto the porous Ca(BO2)2 microspheres, the supported catalyst of 1.05 wt% Pd/Ca(BO2)2exhibited high activity and good recyclability for the selective oxidation of benzylalcohol(Bz OH) to benzaldehyde(BzH), and the conversion of BzOH and selectivity to BzH were confirmed as 94.3% and 96.0%, respectively. In addition, high aspect ratio 1D CaB2O5?H2O nanowires(aspect ratio>500) were obtained by the water-bath-assisted hydrothermal technique. Furthermore, hollowed-out SrB2O4 microspheres derived from the conversion of hydrothermally synthesized hollow SrB2O4?H2O microspheres, demonstrated qm for the adsorption of Pb2+ and Co2+ as456.2 and 619.1 mg g-1, respectively, in contrast however, the adsorption capacities of the hollow SrB2O4?H2O microspheres for Pb2+and Co2+were 244.5 and 558.2 mg g-1,respectively.Apparently, the present hierarchical 3D alkaline-earth metal borates nanoarchitectures were successfully synthesized via a hydrothermal / solvothermal route followed by mild thermal conversion. The as-obtained metal borates nanoarchitectures exhibited advantages over traditional adsorbents and catalyst supports when employed in purifying the simulated waste-water and heterogeneous catalysis, which expanded the novel applications of the alkaline-earth metal borates nano-materials.